fine tuning needles

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sean brady scooters
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Fri Aug 28, 2009 10:02 pm

just to back track a little
apparantly.........simon at B race tuning ...is suppling one off needles for TMX carbs.........
not quite sure exactly what or why.........but there must be a reason i,m sure........
does anyone have more info on these.........? please.
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rog60
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Fri Aug 28, 2009 10:10 pm

Very interesting, all this made me remember a short bit of 'guidence' in the SCK catalogue I have that says and I quote 'The boost bottle, which was invented by Yamaha for the RD350....the effective range of the boost bottle can be varied by altering the length of the connecting tube. Also using a boost bottle allows for a leaner setting of the carb as less fuel is being lost. Fuel economy is significantly improved at low to mid RPM.

At this point the whole concept went straight past me....... :roll: :roll: :roll: :roll: :roll: :roll:
NO IT'S NOT A F***IN* MOPED!!!!!!

J1MS
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Fri Aug 28, 2009 10:30 pm

I really cant agree or disagree with anyone on this as I don't honestly have a solid grasp on the theory involved... I have never cast eyes on any formulas or hard facts I can only speculate but what Sean says about shutting and opening throttles this would be the point the boost bottle gets its biggest pressure change so I can see the thought behind this...
But every single pulse down the inlet tract has a reverberation that will vary as revs & loads increase or decrease, so again I can imagine the boost bottle supplying small boosts between inlet pulses at certain revs again adding a premixed charge on demand... but the one thing I am sure of is its there to compensate for something that cant be found reliably by other means... an enrichment of the inlet charge...
But as I said I really don't understand the formulas & theory involved... But I am sure there are some on this forum with a far greater understanding than most...
Tony, Sean and Al seem to have a good and far better grasp on this than most ... Anyone else have any hard facts (preferably someone that worked on Yamaha's doing R&D in the 80's) What about Terry Sheppard anyone on talking terms with him... That's a man that really knows two strokes....

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sean brady scooters
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Fri Aug 28, 2009 10:55 pm

believe me matey...........boost bottles were used way before the 350 on crossers............... :D
and the idea was that after shutting off quickly from high revs........they stored (temporarially)
a rich instantly available sourse of fuel for rapid wide open throttle acceleration...........but thats all................... :D
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J1MS
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Fri Aug 28, 2009 11:20 pm

sean brady scooters wrote:believe me matey...........boost bottles were used way before the 350 on crossers............... :D
and the idea was that after shutting off quickly from high revs........they stored (temporarily)
a rich instantly available source of fuel for rapid wide open throttle acceleration...........but that's all................... :D
I don't doubt you Sean, as I said I haven't got any real claim to the how's or why's on this subject, and I can as I say, see the reasoning for this as this is when it would get its greatest change in air pressure closed to open throttle.. My knowledge and interest in bikes is not great enough to know when they were first used, but I knew they were around on the early RD's and some earlier TZ's so I mentioned the RD's hoping someone might have some formula to hand... As I said this subject is an education for me... And I see no reason to doubt your explanation... but I do think just by the nature of a two stroke intake (rightly or wrongly) it might also lightly enriches separate areas more or less as well depending on load... but what its original design concept was for I would think is what you have stated... on off throttle use.... to prevent weakening of the mixture.... but surely there will be other aspects that would take an effect from this reserve pulse of stored pressure, as inlet pressure ebbs and flows between pulses...

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sean brady scooters
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Fri Aug 28, 2009 11:27 pm

ok chaps...............
and now that we all agree that certain set ups are a real pain to set up perfectly...............................ie.tuned TS 1,s...JL4,s ..with mikunis............

that leaves us with just what exactly...........?
how are we to overcome this prob.............then....?if not by modifying needles............
i admit that i am perplexed by this situation on certain set ups........as is i think Al............
if only tony or someone could advise us around this i would be very gratefull...........but until this happens.........i can only try every possibility i can think off myself to help.............
hopefully someone ,sooner or later.......that is" in the know".will help us understand and rectify this situation if its possible...........
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sean brady scooters
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Fri Aug 28, 2009 11:46 pm

personally i find the boost bottle thing very interesting...........and do of course take on board everyones views etc regarding this.........
if someone was to try this.........i would be well pleased to allow them to test it out on our dyno............... :D
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J1MS
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Fri Aug 28, 2009 11:58 pm

I will like Sean continue to try to cure lean spots or Hot Spots that cant be jetted out by normal means... by modifying needles if needed, its possibly not the most scientific method, but a modified needle can be replicated close enough if measurements are made and a record kept in case it needs to be repeated... and if it helps to run the scooter cooler then its not a bad thing... But some engines are more awkward depending on setup to get right.... and I don't have a Dyno to help me, so its seat of the pants and plug chops... :roll:... But someone somewhere must have the maths and theory for boost bottles .... there cause and effect...

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tony
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Sat Aug 29, 2009 2:39 am

I dont have as much experience with mikunis as most of you.. I've owned 2 or 3 and sold them all because overall I got better results with the dellorto.
Personally I wouldnt be looking to 'cure' the mikuni when the solution is already out there and its so simple.
The custom needle idea will work i'm sure but you may end up with a stupidly thin needle which could break and wear in no time. And what about replacing the 'custom' needle? You'd have to replicate it instead of simply asking for a k24 or whatever.

The boost bottle idea is really there for other reasons ,not to mask the problems of the carb itself. Also the sizing of the bottle must be right to get any gain. I have never used one (yet) and am certainly not an authority on em tbh.

Btw a bit off topic but I hate how the mikuni's throttle cable attachment works. Thats just amateur to me.
:x
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storkfoot
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Sat Aug 29, 2009 8:29 am

tony wrote: Btw a bit off topic but I hate how the mikuni's throttle cable attachment works. Thats just amateur to me.
:x
Agreed. Only just set up my first Mikuni, a TM24. Carb working really well mind, but what a pain in the @rse when you want to move the needle clip

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